Heat-transfer system for electric transformers or other devices



Feb. 5, 1929. 1,700,839

F. W. GAY

HEAT TRANSFE'T SYSTEM FOR ELECTRIC TRANSFORMERS OR OTHER DEVICES Fil d June 18, 1926 s Sheets-Sheet 1 Zita] iNVENTQR Fragrjlf g g 2- ATTORNEYfi b Feb 5, 1929.

F. W. GAY

HEAT TRANSFER SYSTEM FOR ELECTRIC TRANSFORMERS OR OTHER DEVICES Filed June 18, 1926 3 5heets5heet 'Fehn 5 1929.1 1 70@,839

F. W GAY HEAT TRANSFER SYSTEM FOR ELECTRIC TRANSFORMERS OR OTHER DEVICES Filed June 18, 1926 5 Sheets-Sheet 5 INVENTOR ATTORNEYS n to i r-ii a an FRAZER VJ. GAY, F NEWARK,

Jil in v1 Application filed June 1B, 1929. Serial 116,769.

This invention relates generally to improvements in heat transferring s ysteins tor cooling oil tilled electric transformers or tor other heat extraction operations.

The invention has tor its principal object to provide a novel construction and arrangement 01:? heat transferring or cooling apparatus, which, although adapted for service in connection with other forms and types of mechanical and electrical apparatus, is especially adapted to the cooling oil oil filled electric transformersserving power and lighting circuits.

the past, such oil filled transformers have generally been cooled either by passing cold water through coils in the upper part of the oil jackets or tanks or by radiators located around the sides oi the oil jackets or tanks and connected to the top and bottom of the tank by pipes to promote proper circulation. The first method or" cooling has not been found satisfactory because of the quantity of water required to cool large sizes of transformers as well as by reason of the care necessary to be exercised in order to prevent fr ezing. The second method of self cooling large transformers involves the use of a multiplicity of radiators surrounding the transformers, all of which are connected top and bottom therewith. Such construction requires a large ground space, while at the same time, especially in connection with large size transformers, produces a very unwieldy construction making it necessary to remove or dismantle the radiator elements when shipping the transformers. Due to the restricted ground space generally available for power line transformers which must be located at load centers the radiators are constructed and arranged vertically, and consequently the upper parts of the same are not eiticient incooling function by reason of the tact that the same are bathed in the hot air rising from the lower parts thereof; tiu'thermore, owing to the usually restricted ground space available, it is not possible to provide sullicient radiator 'apacity so that cold oil leaving; the bottom of the raoiator is approximately at the desired ambient temperature when the transformer is continuously loaded one hundred per cent. To obtain great radiator capacity, additional radiators have been placed above the transformer, but this location has been found undesirable by reason of the increased likelihood of oil leakage caused by the increased head of oil.

By the present invention l have sought to provide a cooling or heat transfer system of such novel construction, arrangement, and mode ofoperation as is adapted to overcome the objections above mentioned, while at the same time providing a construction permitting a considerable reduction in the volume or oil required for the transformer while nevertheless permitting greater loads to be carried by the transformer without overheating. To this end my invention broadly coniprises means to apply a refrigerating medium in such manner as to rapidly transfer the heat from the transformer oil bath, in combination with relatively remote radiator means for relieving the refrigerant of absorbed heat and circulating the same in the performance of its cooling function. My invention also includes auxiliary cooling means cooperating with the bottom or lower end of the transformer oil bath, and operating to assist the desired cooling etlects, especially when the transformer is subjected to heavy overload.

Other objects of this invention, not at this time more particularly enumerated, will be clearly understood from the following detailed description of the same.

The invention is clearly illustrated in the accompanying drawings, in which Figure l is in part a front elevation and in part a sectional view of ni novel heattransfer or cooling; apparatus as applied to an electric transformer; Figure 2 is in part a side elevation and in part a sectional view of the same; Figure 3 is an enlarged fragmentary sectional view of the water jacket element of the auxiliary cooling" means for the oil jacket or tank.

Figure l is a sectional view of a modified means for supplying water to the water jacket element oi? the auxiliary cooling means for the oil jacket or tank,

Similar characters of reference are employed in all of the herein described views, to indicate corresponding parts.

Referring now to said drawings, the reference character 10 indicates any suitable type of electric power transformer which is enclosed in the usual oil jacket or tank 11. Spaced between the transformer 10 and the wall of the oil jacket or tank 11 is a battle member 12, the upper end of which termi nates short of the closed top end oi said tank, while the lower end terminates short of the tank bottom, thus providing an inner or ascending circulation path 13 and an outer or descending circulation path l l for the oil in which the transformer is sub merged. Said circulation paths 13 and 1% thus communicating one with the other at.

their upper and lower ends.

Said transformer 10 and the enclosing oil jacket or tank 11 are supported upon a suitable base 15, usually madeot concrete.

Connected with said oil jacket or tank ll, so as to extend around the exterior thereof adjacent to its lower end, is an annular closed receptacle 16, the inner wall of which is prelcrably provided by the wall of said oil jacket or tank ll.

Mounted on the root' or the structure in which the transformer is housed, or in any otherconvenient location, which, if desired, may be more or less remote from the transformer itself, is a radiator member. This radiator member may comprise suitably dise posed headers 17 connected in inter-communieating relation by lateral connecting pipes or ducts l8, and a collector member or pipe 19 which is in a plane beneath said headers 1'7, and which is in communication therewith through a plurality of transversely disposed radiator pipes 20. Connected between the upper end of said receptacle l6 andthe radia' tor headers 17 is vapor delivery pipe 21. Connected between one end of said collector member or pipe 19 and the lower end of said receptacle leis a return pipe Suitably disposed beneath the above described radiator member is a water catch basin and reser- Voir 23 which is connected by pipe-line 2 through a suitable force pump 24 with a' sprinkler head 25 arranged above and adapted to shower the radiator with water when desired, for example, on very hot days, thus increasing the cooling efficiency of the radiator by the evaporation of the water on the surfaces of the radiator pipes 20.

Also connected with said oil jacket or tank 11, so as to extend around the exterior thereof adjacent to its upper end, is a second annular closed receptacle 26. the inner wall of which is preferably provided by the wall of said oil jacket or tank 11. Also mounted on the rool structure in which the transformer is housed,

- transverse radiator pipes 30. Connected between the upper end of said receptacle 26 and the radiator headers 27 is a vapor delivery pipe 31. Connected between one end of said collector member or pipe 29 and the lower end of said receptacle 26 is a return pipe 32.

Connected with the lower end portion of said oil jacket or tank 11, so as to surround the same, is a water acket member- 83 open at its upper end and provided with a marginal lip-portion 3d at its upper periphery. Arranged in the bottom of said Water jacket member 33 is a water supply pipe 35 having outlet orifices 36; said water supply pipe 35 being connected with a feed-pipe 37 leading from a suitable source of -water supply, such, for example, as a city main. Formed in said base 15, or otherwise provided, beneath the lip-portion 34: of said water jacket member is a catch-trough 38 from which leads a suitable drain pipe 39 for leading away the water caught thereby. in rural districts or other locations lacking a water supply system, a modified means for storing and feeding cool water to the water jacket member 33 may be provided. One form of water supply means suitable to such conditions is shown in Figure (5 of the drawings, the same compris-' ing a storage cistern tthleading into the upper end of which is a water supply pipe 421 to deliver water from a suitable source, such as a stream, well or the like. Said supply pipe 41 is preferably provided with a float controlled shut-oil valve 12. Extending upwardly from the bottom of said cistern lO is a cooler pipe 43 which is open at its upper end, said upper end being located below the normal water level of said cistern, so that the warmer water at the said upper level may flow into said upper end of the cooler pipe 43. 'l he lower end of said cooler pipe 43 is provided with an outlet port 4 adjacent the bottom of said cistern. Located within the upper end 01 said cooler pipe 43 is a rcfrigerating element 45, which may be in the form of a tank or receptable, \X'lliljliCOIlllllH-S a suitable retrigcratin medium, such, tor example, as ether. Connected in connnunication with said ether tank or receptacle 45 is a condenser 46 which. is exposed to atmosphere above the cistern, said condenser -16 having an intake conduit l7 and a return conduit l8 suitably connected in connniinication with said ether tank 'lhe cistern is tilled with water, the warmer portion of which, at the upper level of the cistern, will flow into the upper end of the cooler pipe old and in contact with the ether tank 45, to which the heat of the water is transferred, thus causing the ether within the tank 45 to boil. The ether vapors pass upwardly through the intake conduit l? into and through the condenser 46, being thereupon condensed" and returned through the return conduit 48 back to the ether tank l5. The warm water thus entering the upper end of the cooler pipe a8, and becoming chilled by the refrigerating element 45 descends the cooler pipe 43 to pass into the bottom of the cistern through the outlet port 44, displacing warmer water, which rises to the upper level of the cistern for circulation through the cooler pipe 43. In this manner the stored water in the cistern is cooled to approximately the lowest am-v bient temperature occuiringduring the day, so as to be in most efficient condition for use when needed. as will be hereafter more fully described. Connected with the bottom of said cistern 40 is the water feed pipe 37 leading to the water jacket member 33, and if gravity flow is not possible a pump 49 may be provided in the line thereof to compel proper delivery'of the water to said water jacket member 33. If desired, the drain pipe 39 leading from the catch-trough 38 associated with the water jacket member 33, may be led back to the cistern 40,- as indicated in said Figure 6.

For additional cooling effect upon the transformer, when the same is subjected to extra heavy overload, I may also provide a cooling coil 50 arranged in the bottom of the oil jacket or tank 11 for direct contact with the oil content of the latter. Suitable means is provided for circulating through said cooling coil a refrigerating medium;

The operation of the novel heat transfer system in connection with its'appli'cation to electric'power line transformers is as follows. It is understood that by reason of the fluetuating load to which such transformers are subjected, that the generation of heat desired to be dissipated is greatestat those periods in which the transformer is subjected to peak loads and overloads. Power transforn'iers are generally subject to comparatively light loads from about 10 p. m. in the summer until approximately 7 a. m. From 7 a. m. until 5 p. m. they are generally operating under ap proximately full load with a tendency to a slight decrease until dark, but from the fall of darkness until about 10 p. m. the same are running under peak load conditions, and they may during this period be subjected to a very heavy overload for a duration of approximately two hours; Under these conditions the transformer is usually in a comparatively cool condition when thrown on load early in the morning.

.7 Under conditions rising from light loads to approximately full leads, the transfprmer coils will generate more or less heat, which is absorbed by the oil bath in which the same are submerged, the oil being nused to circulate within the oil jacket or tank 11 around the baffle member 12, as the hotoil rises around the inner or transformer side of the latter and the cooler descends down the outer side of the same. Elie receptacle 3.8 which encircles the oil jacket or tank 11 is supplied with a field medium adapted to readily take up heat; for example, ether may be employed as such medium. As the oil heats up, the hotter portions thereof rise to overflow down the outer side of the baffle member 12, and are thus caused to contact with that portion of the oil jacket or tank wall to which the surrounding receptacle 16 applies the ether. The heat of the oil is thereupon transferred through said wall portion to the ether, thereby cooling the oil, and the cool oil descends to pass around the lower end of the bafflemember 12 to again surround the transformer coils to receive the heat generated. by and transferred therefrom. In this manner the circulation of oil is accelerated, while at the same time the heat transferred thereto, is in turn transferred to the cooling medium provided by the other, all of which assures a flow of oil around the transformer coils which is cooled to a temperature adapted to dissipate the heat of the transformer at temperature rises not exceeding :20 degrees C. above ambient temperature. The heat transferred-to the ether in the receptacle 16, causes the same to boil, whereupon the vapor produced ascends through the delivery pipe 21 to the headers 17 of the connected radiator member, such vapors in passing through the radiator pipes 20 being relieved of their heat by radiation to the atmosphere, and thereby being condensed for collection by the collector member 19 for return through the return pipe 22 to the receptacle 16 for repetition ofthecoolingprocessinvolved. Bytheabove described operations, the oil bath around the transformers may be relieved of the heat transferred thereto and kept in practically operative cooling condition so long as the temperature of the hot oil at the top of the jacket or tank 11 remains under degrees (1, and consequently the transformer is relieved of heat under fluctuating load conditions from light to approximately full loads, and under moderate atmospheric temperature. If, by reason of excess generation of heat in the transformer, or by reason of appreciable rises of atmospheric temperature, the temperature of the hot oil of the jacket or tank 11 rises above 50 degrees (1, additional cooling or heat tranferring means is automatically brought into action. This additional means comprises the receptacle 26 which surrounds the upper part of the. oil jacket or tank 11, and in which introduced a fluid medium operative at higher temperatures to take up heat; such a fluid medium as alcohol may be employed in this connection. When the temperature of the oil at the top of the jacket or tank 11 rises to 50 degrees C. or more up to approximately degrees C., the contact of the hot oil with that portion of the jacket or tank wall coincident to the receptacle 26 will permit the transfer of heat from the oil through the wall to the alcohol in said receptacle 26, whereby the temperature of theoil is reduced, while being subject Ill) lli'i to further reduction when passing the zone of the ether receptacle 16, so that by the time it returns to the bottom of the jacket or tank for up-flow around the transformer coils it has been cooled down to approximately degrees C. when ambient temperature is about 40 degrees C. The transfer of heat to the alcohol in the receptacle 26 causesthe same to boil, whereupon the vapors produced will ascend the delivery pipe 81 to the headers 27 of the connected radiator member, to flow through the radiator pipe 30 through which the heat thereof is dissipated by radiation thus condensing the alcohol for collection in the-eolle'ctorinember 29, to be thence returned through the return pipe 32 to the receptacle 26 for repetition of the cooling processes involved. If the temperature of the hot oil approximates degrees (3., it is advisableto start the pump 24: supplying the water spray over the radiator member elements 17, 18, 19, 20, whereby the efiiciency thereof is greatly increased, and the cooling elfect of the ether medium in the receptacle 16 is maintained efiiciently operative.

From the above description it will be apparent that my novel system of heat transfer or cooling devices will automatically operate to dissipate the undesired heat generated by electric power transformers under varying conditions and under loads varyingfrom light loads to full loads, and even under overloads of comparatively short duration.

Under conditions of heavy overloads, espccially when the same are of appreciable duration, 1 have found it desirable to provide additional auxiliary cooling means already above described, which may be brought into operation at will according to need, and which function as follows. By this auxiliary cooling means wateris circulated through the water jacket member on from a suitable source of supply as already above set forth. Cool water is delivered to the water supply pipe in the bottom of said jacket member 33, and is discharged into the interior of the latter through the orifices 36 in said supply pipe. The water fills the jacket member 33 so as tn surround the lower portion of the oil jacket or tank 11, whereby additional heat may be absorbed from the cooled oil descending the outer side of the balllc member 1;, for up-iiow around the hot transformer co'ils. The additional heat thus transferred to the water is carried off thereby. as the water overflows the lip-portion M of the water-jacket 83, and the 'arm water is replaced by the incoming cool water. This additional cooling effect enables the transformer to carry a heavy overload, and yet, owing to cooling of the oil by the main cooling elements, attains the desired additional cooling etl'ect with a comparatively small lift in temperature thus making for economy.

Still. further cooling etiects under high heavy overload conditions of the transformer,

time is permitted during relatively normal load conditions or, off peak hours to reduce the cooling medium, which may be water or brine, to approximately freezing temperature, and thus to store its capacity for absorbing heat ready for application during peak hours.

It will be understood that in the accompanying drawings and the above specification, the invention has been shown and described merely in preferred form and by way of example and as applied more especially to electric power transformers, but obviously many alterations and variations may be made therein and in its mode of application which will still be comprised within its spirit For instance I may wish to employ a refrigerant having a low boiling point in all of the aforesaid cooling means, thus keeping the temperature of the transformer relatively close to the temperature of the ambient air during off peak hours; or I may employ a refrigerant in all the cooling means having a relatively high boiling point, e. g. approximately 10 degrees C., so that at very low ambient temperatures, e. g. minus 80 degrees C. or less, the cooling means will not circulate, but will actually act as a heat insulator to maintain a relatively high transformer temperature during off peak loads, and thereby prevent extreme ten'iperature changes in the transformer with consequent tendency to mechanical shrinkage and expansion strains. Generally s )eaking, therefore, it is to be understood that this invention is not limited to any specilic form or adaptation except in so far as such limitations may be specified in the claims.

I wish to here emphasize the following advantages which I attribute to my present in vention.

First. The radiators may be located more or less remotely from the apparatus to be cooled, and in the most ellicient and economical situation, thus permitting the transformer to be installed in a pit or basement-if tltSH'Otl.

Second. liy the use of two or more separate annular cooling zones or recc )taclcs in, association with the apparatus to be cooled, each provided with a corresponding radiator, and the same being respectively provided with suitable refrigerants, I am able to effect two or more temperatures of radiation, the higher temperature refrigerant being adapted to dissipate most of the heat in a cheap and economical manner, while the lower tempcraturc re frigerant is effective not so much to extract large quantities of heat as to pull down the temperature of the bottom oil.

Third. By my system l provide means for storing up the coolest available ambient temperature which will generally occur at off peak load periods-when it is not needed, so that the same is available for use during a peak ambient temperature or during a peak load period or both; and, furthermore, I provide means for using this stored cold medium to obtain the last few degrees of bottom oil cooling, returning the cold medium to its place of storage with only a relatively small lift in temperature, whereby the coolest ambient temperature which occurs at off peak conditions will be required to extract only a few degrees of heat.

Fourth. By using my novel low tempera-, ture brine tank I may greatly increase the overload capacity of a transformer by supplying to the transformer coils oil of very low temperature.

Fifth. By a choice of suitable refrigerant or refrigerants I may cause such refrigerant to serve as a heat insulator at low tempera-' tures while at the same time becoming a very effective cooling agent at high temperatures.

Havingthus described my invention, I claim 1. In combination with an apparatus having a circulating fluid to be cooled, independent means for applying refrigerants in separate volumes respectively in contact with different portions of said apparatus to which heat from said circulating fluid may be transferred at diti'erent temperatures, one said means being located adjacent the zone of maximum heat to serve as a means to step down maximum temperature of said circulating fluid, the other said means being located at a position accordin to the direction of circulation of the fluid to be cooled adapted to further reduce the temperature of the fluid adjacent the low temperature oint of its circulation, a radiator means 'or each volume of refrigerant, means for conducting the vapor of each volume of refrigerant to the radiator corresponding thereto, and means to return each condensed refrigerant respectively in contact with the respective portions of said apparatus served thereby as aforesaid.

2. In combination with an electric transformer, an enveloping tank containing oil,

3. lo. combination with an electric trans former, an enveloping tank containing oil, means for applying a refrigerant in juxtaposition with said oil to which heat from said oil may be transferred, a radiator means, and means for conducting the vapor of the refrigerant to said radiator to be relieved of its heat and condensed, means to return the condensed refrigerant to said means in juxtaposition with said oil, and means cooperative with said radiator to shower the same with water to obtain additional cooling effects of evaporation.

4. In combination with an electric transformer having an enveloping oil jacket the oil content of which is subject to circulation, means for partially cooling said oil, means for applying a refrigerant in uxtaposition with said partially cooled oil to which heat from said partially cooled oil may be transferred, a radiator means, means for conducting the vapor of the refrigerant to said radiator means to be relieved of its heat and condensed,

and means to return the condensed refrigerant to said means in juxtaposition with said partially cooled oil.

5. In combination with an electric transformer having an enveloping oil jacket the oil content of which is subject to circulation, means for partially extracting the heat from said oil, means for storing an additionalreserve cooling medium so that it may yield its heat to the ambient air when the latter is at a minimum temperature, means to retain said reserve cooling medium at a minimum temperature under rising ambient a i r temperature, and means for applying the heat absorbing capacity of said reserve cooling medium more or less rapidly to reduce the temperature of said oil during relatively short peak overload conditions of said transformer.

6. In combination with an electric power transformer, an enveloping tank containing oil subject to convective circulation, an exterior receptacle around said tank arranged to hold a refrigerant in contact with the tank wall to thereby extract heat from said oil. a radiator means. means for conducting the vapor of the refrigerant to said radiator to be relieved of its heat and condensed, and means to return the condensed refrigerant to said receptacle.

7. In combination with an electric power transformer, an enveloping tank containing oil subject to convective circulation, a plurality of independent annular receptacles vertit-ally spaced around said tank and rcspeclively adapted to hold refrigerants effective at differenttemperatures proportional to the differences in temperature of the circulating oil, a radiator means for ach refrigerant, means for conducting the vapor of each refrigerant to its corresponding radiator to be relieved of its heat and condensed, and means intermediate each radiator and receptacle for returnin the condensed refrigerants thereto.

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8. In combination with an electric power transformer, an enveloping tank containing oil subject to convective circulation, means cooperative with said tank wall for extracting heat from said oil by conduction and radiation to the, ambient air, and auxiliary cooling means for further reducing the oil temperature below ambient air temperature at the desired low tem ierature point of its circulation.

9. In combination with an electric. transformer, an enveloping tank containing oil, said tank having an annular baflie member intermediate said transformer and tank wall to control convective circulation of said oil, means cooperative with saidtank wall for extractingih ent from said oil by conduction and radiation to ambient air, means for storing an additional, reservecooling medium so that it may yield its heat to t e ambient air when the latter isiat a minimum" emperature, means retaining saidreserve cooling medium at minifrom its oil content, a radiator means, means for conducting the vapor to the refrigerant to said radiator means to be relieved of its heat and condensed, means to return the condensed refrigerant to said receptacle, and means. cooperative with said radiator to shower the latter with water to obtain additional cooling effects of eva oration.

11. In com ination with an electric transformer having an enveloping oil jacket the oil content of which is subject to circulation, an exterior receptacle around said tank arranged to hold a refrigerant in contact with the tank wall to thereby extract heat from itsoil content, a radiator means, means for conducting the vapor of the refrigerant to said radiatormcans to be relieved of its heat and condensed, means to return the condensed refrigerant to said receptacle, means for storing an additional reserve cooling medium so that it may yield its heat to the ambient air when the latter is at a minimum temperature, means retaining said reserve cooling medium at minimum temperature under rising ambient air temperature, and means for using the heat absorbing capacity of saidrescrvc cooling, medium more or less rapidly to reduce the temperature of said oil during relatively short peak overload conditions of said transformer. l v 12. In combination with an electric transcles vertically spaced around said tank and respectively adapted to hold refrigerants effective at diiferent temperatures proportional to the differences in temperature of the circulating oil, a radiator corresponding to each receptacle and in communication therewith, and auxiliary cooling means for further reducing the oil temperature at the desired low temperature point of its circulation. I a v 13. In combination with an electric "transformer having an enveloping oil jacket the oil content of which is subject to circulation, a plurality of independent annular receptacles vertically spaced around said tank and respectively adapted to hold refrigerants effective at different temperatures proportional to the difi'erences in temperature of the circulating oil, a radiator corresponding to each receptacle and in communication therewith, means for storing an additional reserve cooling medium so that it may yield its heat to the ambient air when the latter is at a minimum temperature, means retaining said reserve cooling medium at minimum temper- 'ature under rising ambient air temperature, and means for using the heat absorbing capacity of said reserve coolin medium more or less rapidly to reduce the temperature of said oil 1 during relatively short peak overload conditions of said transformer.

14. In combination with an electric trans-4 former having an envelo i'ng oil jacket the oil content of which is su ject to circulation, a plurality of independent annular receptacles vertically spaced around said tank and respectively adapted to hold refrigerants effective at different temperatures proportional to the differences in temperature of the circulating oil, a radiator corresponding to each receptacle anddn communication therewith, a water jacket surrounding thelower end of said oil jacket, and means for circulating cool water therethrough.

15. In combination with an electric transformer having an enveloping oil jacket the oil content of which is subject to circulation, a plurality of independent annular receptacles vertically spaced around said tank and respectively adapted to hold refrigerants effective at different temperatures proportional to the differences in temperature -of the circulating oil, a radiator corresponding to each receptacle and in communication therewith, a water jacket surrounding the lower end of said oil jacket, means for circulating cool Water therethrough, a cooling pipe coil within the lower end of said oil jacket in contact with the oil content thereof, means for storing a supply of reserve cooling medium for circulation through said cooling pipe cpil, and means for controlling at will the circulation of saidreserve cooling medium through said cooling pipe coil.

16. In combination With an electric transformer having an enveloping oil jacket the oil content of which is subject to circulation, a plurality of independent annular receptacles vertically spaced around said tank and respectively adapted to hold refrigerants effective at different temperatures proportional to the differences in temperature of the circulating oil, a radiator corresponding to 17; In combination with an electric transformer having an enveloping oil jacket the oil content of which is subject to circulation, a plurality of independent annular receptacles vertically spaced around said tank and respectively adapted to hold refrigerants effective at different temperatures proportional to the differences in temperature of the circulating oil, a radiator corresponding to each receptacle and incommunication therewith, a cooling pipe coil Within the lower end of said oil jacket in contact with the oil content thereof, means for storing a supply of reserve cooling medium for circulation through said cooling pipe coil, means for dissipating heat from said stored supply when said cooling pipe coil is inactive, and means for controlling at will delivery of said reserve cooling medium through said cooling pipe coil, a water jacket surrounding the lower end of said oil jacket, and means for circulating cool water therethrough.-

.18. In combination with an electric transformer, an enveloping tank containing oil for circulation therein relative to said transformer, means for applying a volatile liquid in juxtaposition With said oil whereby the former by its evaporation is adapted to extract heat from the latter, a radiator means for cooling and condensing the vapor of said volatile liquid, means to return the condensed volatile liquid to said means for applying the same in juxtaposition with said oil, and 11183119110 circulate cold Water in juxtaposition with saidoil at the desired low temperature pointof the circulation of the latter.

In testimony, that I claim the invention set fiorth above I have hereunto set my hand this 12th day of June, 1926.

' FRAZER W. GAY. 

